I have always been using the Arduino Nano with my MacBook Pro (10.6. and it shows all the Serial Ports when the connected, still now.

Now I connected the same setup via USB to a MacBook Air (10.8.2) and it shows only Bluetooth ports and then to an iMac (10.6. and there it again only shows Bluetooth. When trying with an Uno it works all fine.

Am I missing something? Why does it work on one computer and on another with even the same OS not anymore?